Inbreeding avoidance

Inbreeding avoidance, or the inbreeding avoidance hypothesis, is a concept in evolutionary biology that refers to the prevention of the deleterious effects of inbreeding. Animals only rarely exhibit inbreeding avoidance.[1] The inbreeding avoidance hypothesis posits that certain mechanisms develop within a species, or within a given population of a species, as a result of assortative mating and natural and sexual selection, in order to prevent breeding among related individuals. Although inbreeding may impose certain evolutionary costs, inbreeding avoidance, which limits the number of potential mates for a given individual, can inflict opportunity costs.[2] Therefore, a balance exists between inbreeding and inbreeding avoidance. This balance determines whether inbreeding mechanisms develop and the specific nature of such mechanisms.[3]

A 2007 study showed that inbred mice had significantly reduced survival when they were reintroduced into a natural habitat.[4]

Inbreeding can result in inbreeding depression, which is the reduction of fitness of a given population due to inbreeding. Inbreeding depression occurs via appearance of disadvantageous traits due to the pairing of deleterious recessive alleles in a mating pair's progeny.[5] When two related individuals mate, the probability of deleterious recessive alleles pairing in the resulting offspring is higher as compared to when non-related individuals mate because of increased homozygosity. However, inbreeding also gives opportunity for genetic purging of deleterious alleles that otherwise would continue to exist in population and could potentially increase in frequency over time. Another possible negative effect of inbreeding is weakened immune system due to less diverse immunity alleles as a result of outbreeding depression.[6]

A review of the genetics of inbreeding depression in wild animal and plant populations, as well as in humans, led to the conclusion that inbreeding depression and its opposite, heterosis (hybrid vigor), are predominantly caused by the presence of recessive deleterious alleles in populations.[7] Inbreeding, including self-fertilization in plants and automictic parthenogenesis (thelytoky) in hymenoptera, tends to lead to the harmful expression of deleterious recessive alleles (inbreeding depression). Cross-fertilization between unrelated individuals ordinarily leads to the masking of deleterious recessive alleles in progeny.[8][9]

Many studies have demonstrated that homozygous individuals are often disadvantaged with respect to heterozygous individuals.[10] For example, a study conducted on a population of South African cheetahs demonstrated that the lack of genetic variability among individuals in the population has resulted in negative consequences for individuals, such as a greater rate of juvenile mortality and spermatozoal abnormalities.[11] When heterozygotes possess a fitness advantage relative to a homozygote, a population with a large number of homozygotes will have a relatively reduced fitness, thus leading to inbreeding depression. Through these described mechanisms, the effects of inbreeding depression are often severe enough to cause the evolution of inbreeding avoidance mechanisms.[12]

  1. ^ de Boer, Raïssa A.; Vega-Trejo, Regina; Kotrschal, Alexander; Fitzpatrick, John L. (July 2021). "Meta-analytic evidence that animals rarely avoid inbreeding". Nature Ecology & Evolution. 5 (7): 949–964. Bibcode:2021NatEE...5..949D. doi:10.1038/s41559-021-01453-9. ISSN 2397-334X. PMID 33941905. S2CID 233718913.
  2. ^ Waser PM, Austad SN, Keane B (1986). "When should animals tolerate inbreeding?". American Naturalist. 128 (4): 529–537. doi:10.1086/284585. S2CID 84806782.
  3. ^ Archie EA, Hollister-Smith JA, Poole JH, Lee PC, Moss CJ, Maldonado JE, Alberts SC (2007). "Behavioural inbreeding avoidance in wild African elephants". Molecular Ecology. 16 (19): 4138–4148. Bibcode:2007MolEc..16.4138A. doi:10.1111/j.1365-294x.2007.03483.x. PMID 17784925. S2CID 1535829.
  4. ^ Jiménez JA, Hughes KA, Alaks G, Graham L, Lacy RC (October 1994). "An experimental study of inbreeding depression in a natural habitat". Science. 266 (5183): 271–273. Bibcode:1994Sci...266..271J. doi:10.1126/science.7939661. PMID 7939661.
  5. ^ Mohammad Afzal (January 1983). "Consanguinity effects on Intelligence Quotient and neonatal behaviors of Ansari muslim children".
  6. ^ Sommer, S. (2005). "The importance of immune gene variability (MHC) in evolutionary ecology and conservation". Frontiers in Zoology. 2: 16. doi:10.1186/1742-9994-2-16. PMC 1282567. PMID 16242022.
  7. ^ Charlesworth D, Willis JH (2009). "The genetics of inbreeding depression". Nat. Rev. Genet. 10 (11): 783–96. doi:10.1038/nrg2664. PMID 19834483. S2CID 771357.
  8. ^ Bernstein H, Hopf FA, Michod RE (1987). "The Molecular Basis of the Evolution of Sex". Molecular Genetics of Development. Advances in Genetics. Vol. 24. pp. 323–70. doi:10.1016/s0065-2660(08)60012-7. ISBN 9780120176243. PMID 3324702.
  9. ^ Michod, R.E. (1994). "Eros and Evolution: A Natural Philosophy of Sex" Addison-Wesley Publishing Company, Reading, Massachusetts. ISBN 978-0201442328
  10. ^ Crnokrak P, Roff DA (1999). "Inbreeding depression in the wild". Heredity. 83 (3): 260–270. doi:10.1038/sj.hdy.6885530. PMID 10504423.
  11. ^ O'Brien SJ, Roelke ME, Marker L (1985). "Genetic basis for species vulnerability in the cheetah". Science. 227 (4693): 1428–1434. Bibcode:1985Sci...227.1428O. doi:10.1126/science.2983425. PMID 2983425. S2CID 14341795.
  12. ^ Pusey A, Wolf M (1996). "Inbreeding avoidance in animals". Trends Ecol Evol. 11 (5): 201–206. Bibcode:1996TEcoE..11..201P. doi:10.1016/0169-5347(96)10028-8. PMID 21237809.